Liquid crystal display device and television set

ABSTRACT

A liquid crystal display device includes a liquid crystal display panel, and a backlight unit. The backlight unit includes a plurality of light emitting diodes each having an anode and a cathode, and first adjacently and disposed substrates. The plurality of light emitting diodes are mounted on the first substrate and the second substrate and arranged in a plurality of rows. A first light emitting diode mounted on the first substrate and a second light emitting diode mounted on the second substrate which are adjacent across a boundary between the first substrate and the second substrate are disposed so that respective anodes of the first and second light emitting diodes are opposed to each other and have a pitch equal to or smaller than a pitch of other light emitting diodes mounted on the first and second substrates.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/170,258, filed Jun. 28, 2011, the contents of which are incorporatedherein by reference.

The present application claims priority from Japanese application JP2010-146547 filed on Jun. 28, 2010, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device.

2. Description of the Related Art

Light emitting diodes (LEDs) have become widely used as light sources ofa backlight unit. For example, there is known an edge light typebacklight unit in which, instead of cold-cathode tubes, light emittingdiodes are disposed on an end surface of a light guide plate so as toenable surface emission by the light guide plate. Further, there isknown an example using light emitting diodes in a direct type backlightunit (Japanese Patent Application Laid-open No. 2009-87879).

In a conventional direct type or edge type backlight unit, the lightemitting diodes are generally arranged evenly or at equal intervals.With this arrangement, heat generated from the light emitting diodes isuniform inside the backlight unit.

However, in recent years, even in the direct type backlight unit, therehas been a demand that the light emitting diodes be disposed on asubstrate which is much smaller in size compared with a liquid crystalpanel. In such a case, the light emitting diodes are arranged at unequalpitches in some cases in view of the luminous efficiency. In such acase, heat generation inevitably increases at a portion where the lightemitting diodes are provided close to one another. Therefore, somecountermeasure against heat is required.

SUMMARY OF THE INVENTION

The present invention has an object to provide a liquid crystal displaydevice provided with a countermeasure against heat in a backlight unit.

(1) A liquid crystal display device according to the present inventionincludes: a liquid crystal display panel; and a backlight unit, inwhich: the backlight unit includes: a plurality of light emitting diodeseach having an anode and a cathode; a first substrate; and a secondsubstrate, the plurality of light emitting diodes being mounted on thefirst substrate and the second substrate; the first substrate and thesecond substrate are disposed adjacent to each other; light emittingdiodes, which are adjacent across a boundary between the first substrateand the second substrate, of the plurality of light emitting diodes aredisposed so that the respective anodes are opposed to each other and soas to have a pitch equal to or smaller than a pitch of other adjacentlight emitting diodes of the plurality of light emitting diodes.According to the present invention, a pair of the light emitting diodeshaving a small pitch are disposed so that respective anodes are opposedto each other. Therefore, the respective cathodes, at which heat iseasily generated, are kept away from each other, and hence it ispossible to avoid heat concentration.

(2) In the liquid crystal display device as described in Item (1) of thepresent invention: light emitting diodes, which are mounted on the firstsubstrate, of the plurality of light emitting diodes may all be arrangedso that the cathodes thereof face a side opposite to the secondsubstrate; and light emitting diodes, which are mounted on the secondsubstrate, of the plurality of light emitting diodes may all be arrangedso that the cathodes thereof face a side opposite to the firstsubstrate.

(3) In the liquid crystal display device as described in Item (2) of thepresent invention: the light emitting diodes mounted on the firstsubstrate may be arranged in a direction separating from the secondsubstrate and may be electrically connected in series; and the lightemitting diodes mounted on the second substrate may be arranged in adirection separating from the first substrate and may be electricallyconnected in series.

(4) The liquid crystal display device as described in Item (3) of thepresent invention may further include: a first connector, which ismounted at an end portion of the first substrate on a side opposite tothe second substrate; first cathode wiring, which electrically connectsthe first connector and the cathode of the light emitting diode which isfarthest from the second substrate among the light emitting diodeselectrically connected in series on the first substrate; first anodewiring, which electrically connects the first connector and the anode ofthe light emitting diode which is closest to the second substrate amongthe light emitting diodes electrically connected in series on the firstsubstrate; a second connector, which is mounted at an end portion of thesecond substrate on a side opposite to the first substrate; secondcathode wiring, which electrically connects the second connector and thecathode of the light emitting diode which is farthest from the firstsubstrate among the light emitting diodes electrically connected inseries on the second substrate; and second anode wiring, whichelectrically connects the second connector and the anode of the lightemitting diode which is closest to the first substrate among the lightemitting diodes electrically connected in series on the secondsubstrate.

(5) In the liquid crystal display device as described in Item (4) of thepresent invention: the plurality of light emitting diodes may berespectively arranged on the first substrate and the second substrate ina plurality of rows; the first anode wiring may be disposed so as topass between the plurality of light emitting diodes arranged in theplurality of rows on the first substrate; and the second anode wiringmay be disposed so as to pass between the plurality of light emittingdiodes arranged in the plurality of rows on the second substrate.

(6) In the liquid crystal display device as described in Item (4) of thepresent invention: the plurality of light emitting diodes may berespectively arranged on the first substrate and the second substrate ina plurality of rows; the first anode wiring may be disposed so as topass one of regions opposing across all of the plurality of lightemitting diodes arranged in the plurality of rows on the firstsubstrate; and the second anode wiring may be disposed so as to pass oneof regions opposing across all of the plurality of light emitting diodesarranged in the plurality of rows on the second substrate.

(7) In the liquid crystal display device as described in Item (4) of thepresent invention: the light emitting diodes mounted on the firstsubstrate may be arranged in one row; and the light emitting diodesmounted on the second substrate may be arranged in one row.

(8) The liquid crystal display device as described in Item (3) of thepresent invention may further include: a connector, which is mounted atan end portion of the first substrate on a side opposite to the secondsubstrate; anode wiring, which is formed on the first substrate and thesecond substrate so as to electrically connect the connector and theanode of the light emitting diode which is closest to the secondsubstrate among the light emitting diodes electrically connected inseries on the first substrate and so as to electrically connect theconnector and the anode of the light emitting diode which is closest tothe first substrate among the light emitting diodes electricallyconnected in series on the second substrate; first cathode wiring, whichelectrically connects the connector and the cathode of the lightemitting diode which is farthest from the second substrate among thelight emitting diodes electrically connected in series on the firstsubstrate; and second cathode wiring, which is formed on the firstsubstrate and the second substrate so as to electrically connect theconnector and the cathode of the light emitting diode which is farthestfrom the first substrate among the light emitting diodes electricallyconnected in series on the second substrate.

(9) The liquid crystal display device as described in Item (8) of thepresent invention may further include a relay connector, which connectsa part of the anode wiring on the first substrate and a part of theanode wiring on the second substrate and connects a part of the secondcathode wiring on the first substrate and a part of the second cathodewiring on the second substrate.

(10) In the liquid crystal display device as described in Item (8) or(9) of the present invention: the plurality of light emitting diodes maybe respectively arranged on the first substrate and the second substratein a plurality of rows; and the anode wiring and the second cathodewiring may be disposed so as to pass one of regions opposing across allof the plurality of light emitting diodes arranged in the plurality ofrows on the first substrate and the second substrate.

(11) In the liquid crystal display device as described in Item (8) or(9) of the present invention: the plurality of light emitting diodes maybe respectively arranged on the first substrate and the second substratein a plurality of rows; the anode wiring may be disposed so as to passbetween the plurality of light emitting diodes arranged in the pluralityof rows on the first substrate; and the second cathode wiring may bedisposed so as to pass one of regions opposing across all of theplurality of light emitting diodes arranged in the plurality of rows onthe first substrate and the second substrate.

(12) In the liquid crystal display device as described in any one ofItems (1) to (11) of the present invention, the plurality of lightemitting diodes may be arranged in a staggered pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a cross-sectional view illustrating a basic structure of aliquid crystal display device according to an embodiment mode of thepresent invention;

FIG. 2 is a plan view of a backlight unit;

FIG. 3 is a view illustrating a reflection sheet, which corresponds to astructure in which light emitting diodes are arranged;

FIG. 4 is a top view of a substrate;

FIG. 5 is a wiring diagram of a first substrate and a second substrateof a liquid crystal display device according to a first embodiment ofthe present invention;

FIG. 6 is a wiring diagram of a first substrate and a second substrateof a liquid crystal display device according to a modified example ofthe first embodiment of the present invention;

FIG. 7 is a wiring diagram of a first substrate and a second substrateof a liquid crystal display device according to a second embodiment ofthe present invention;

FIG. 8 is a wiring diagram of a first substrate and a second substrateof a liquid crystal display device according to a third embodiment ofthe present invention;

FIG. 9 is a wiring diagram of a first substrate and a second substrateof a liquid crystal display device according to a modified example ofthe third embodiment of the present invention;

FIG. 10 is an exploded perspective view of a liquid crystal televisionset according to a fourth embodiment of the present invention;

FIG. 11 is a view illustrating members provided behind a reflectionsheet of the liquid crystal television set illustrated in FIG. 10;

FIG. 12 is a side view of the liquid crystal television set illustratedin FIG. 10;

FIG. 13 is a schematic view of a vertical cross section of the liquidcrystal television set illustrated in FIG. 10;

FIG. 14 illustrates a light intensity distribution of a point lightsource; and

FIG. 15 is a graph illustrating a measurement result of intensity oflight which exits from a lens.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment mode of the present invention is describedwith reference to the drawings.

[Basic Structure]

FIG. 1 is a cross-sectional view illustrating a basic structure of aliquid crystal display device according to the embodiment mode of thepresent invention.

The liquid crystal display device includes a liquid crystal displaypanel 10. The liquid crystal display panel 10 has a display surface(left surface in FIG. 1) and a rear surface (right surface in FIG. 1),which is on a side opposite to the display surface. A plurality ofoptical sheets 12, such as a diffusion sheet and a prism sheet, aredisposed so as to be opposed to the rear surface of the liquid crystaldisplay panel 10.

The liquid crystal display device includes a backlight unit 14. FIG. 2is a plan view of the backlight unit 14. The optical sheets 12 aredisposed between the liquid crystal display panel 10 and the backlightunit 14. The backlight unit 14 includes a plurality of light emittingdiodes 16 serving as light sources. The plurality of light emittingdiodes 16 are mounted on a substrate 18 made of a glass epoxy resin orthe like. The substrate 18 has a surface on which the plurality of lightemitting diodes 16 are mounted, which is opposed to the rear surface(right surface in FIG. 1) of the liquid crystal display panel 10.

A reflection sheet 20 overlaps the substrate 18 at the surface on whichthe plurality of light emitting diodes 16 are mounted in a mannerwithout overlapping the plurality of light emitting diodes 16. Thereflection sheet 20 is larger in size than the substrate 18, and theentire substrate 18 is overlapped with a part of the reflection sheet20. The reflection sheet 20 is made of, for example, a whitepolyethylene terephthalate (PET) resin. The reflection sheet 20 is madeof a material having a rate of thermal expansion that is different fromthat of the material of the substrate 18. The reflection sheet 20 hashigher light reflectance than the surface of the substrate 18. Asillustrated in FIG. 1, the reflection sheet 20 is folded or bent so asto avoid being parallel to the rear surface (right surface in FIG. 1) ofthe liquid crystal display panel 10. In this manner, directions of lightbeams reflected by the reflection sheet 20 are adjusted.

The substrate 18 on which the light emitting diodes 16 are mounted isattached to a support plate 22. The support plate 22 is fixed to abottom surface of a box-shaped housing 24 on an inner side thereof. Thesupport plate 22 functions as a radiator plate. End portions of thereflection sheet 20 are attached to peripheral portions on the innerside of the housing 24.

The liquid crystal display panel 10 and the substrate 18 each have ashape in which a common width in a first direction D₁ (directionvertical to the sheet plane of FIG. 1 and right-and-left direction inFIG. 2) is longer than a width in a second direction D₂ (up-and-downdirection in FIG. 1 or FIG. 2), which is orthogonal to the firstdirection D₁. For example, each of the liquid crystal display panel 10and the substrate 18 has a rectangular shape which is long in the firstdirection D₁ in plan view.

As illustrated in FIG. 1, a width of the substrate 18 in the seconddirection D₂ is shorter than a width of the liquid crystal display panel10 in the second direction D₂. The width of the substrate 18 in thesecond direction D₂ is one-third the width of the liquid crystal displaypanel 10 in the second direction D₂ or less. The substrate 18 is opposedto, while avoiding being opposed to both end portions of the liquidcrystal display panel 10 in the second direction D₂, a central portionbetween the both end portions of the liquid crystal display panel 10.

FIG. 3 is a view illustrating a reflection sheet 20 a, which correspondsto the structure in which the light emitting diodes 16 are arranged. Thereflection sheet 20 a has a plurality of holes 26 formed therein so asto dispose the plurality of light emitting diodes 16 one by one on theinner side thereof. The plurality of holes 26 correspond to thearrangement of the light emitting diodes 16 illustrated in FIG. 2, andare arranged in a staggered pattern in the first direction D₁. Theplurality of holes 26 are arranged at unequal pitches.

The reflection sheet 20 a has a flat region 28, which is opposed andparallel to the substrate 18. The plurality of holes 26 are formed inthe flat region 28. The reflection sheet 20 a further has first inclinedregions 30 provided continuously with the flat region 28 in an inclinedmanner. The first inclined regions 30 are respectively providedcontinuously with a pair of sides extending in the first direction D₁ ofthe flat region 28. The reflection sheet 20 a is folded so thatboundaries are observable between the flat region 28 and the firstinclined regions 30. In each of the first inclined regions 30, a surfaceon a side opposite to the substrate 18 (surface on which light isreflected) is curved so as to become a recess surface.

The reflection sheet 20 a further has second inclined regions 32provided continuously with the flat region 28 in an inclined manner. Thesecond inclined regions 32 are respectively provided continuously with apair of sides extending in the second direction D₂ of the flat region28. The reflection sheet 20 a is folded so that boundaries areobservable between the flat region 28 and the second inclined regions32. One second inclined region 32 is positioned between a pair of thefirst inclined regions 30, and one first inclined region 30 ispositioned between a pair of the second inclined regions 32.

FIG. 4 is a top view of the substrate 18. The plurality of lightemitting diodes 16 are arranged in two rows in the first direction D₁.The plurality of light emitting diodes 16 are arranged in a staggeredpattern. Further, pitches between adjacent light emitting diodes 16 areunequal.

In this embodiment mode, the substrate 18 is divided into two substratesat a central portion thereof. In other words, the substrate 18 includesa first substrate 18-1 and a second substrate 18-2. This is because, ina liquid crystal television set or the like having a large screen, it isdifficult to form the substrate 18 in an integrated manner. Division ismade in order to facilitate the manufacturing steps. On the firstsubstrate 18-1 or the second substrate 18-2, a connector 19 is mounted,to which wiring extended from an inverter circuit (not shown) for lightsource is connected. The first substrate 18-1 and the second substrate18-2 are connected to each other, and the connector 19 is provided oneach end portion of the connected first substrate 18-1 and secondsubstrate 18-2. Further, the first substrate 18-1 and the secondsubstrate 18-2 are formed in a point symmetric shape, and may be formedin the same shape.

Here, temperature characteristics of the light emitting diodes 16 aredescribed. Each of the light emitting diodes 16 includes two terminalsof an anode and a cathode. Generally, as for the temperaturecharacteristics, the cathode side has a higher temperature. Althoughthis is not a uniform characteristic and depends on a material andenvironment at the periphery, there is a case where one light emittingdiode 16 has a temperature difference of few degrees between the anodeand the cathode thereof.

In a case where the light emitting diodes 16 are uniformly arranged,there is little problem about the difference in heat generationtemperature between the anode side and the cathode side. However, in acase where the light emitting diodes 16 are arranged at unequal pitchesas in the example illustrated in FIG. 4, there are places where unequalheat generation occurs. Therefore, a countermeasure is required.

First Embodiment

FIG. 5 is a wiring diagram of the first substrate 18-1 and the secondsubstrate 18-2 of a liquid crystal display device according to a firstembodiment of the present invention.

In this embodiment, the substrate 18 includes the first substrate 18-1and the second substrate 18-2. The first substrate 18-1 and the secondsubstrate 18-2 are disposed adjacent to each other. The plurality oflight emitting diodes 16 are mounted on the first substrate 18-1 and thesecond substrate 18-2.

Note that, in FIG. 4, the light emitting diodes 16 are in a staggeredarrangement and the arrangement intervals thereof are unequal pitches.However, in FIG. 5, in order to simplify the illustration, a case wherethe arrangement intervals thereof are equal pitches is illustrated.Further, a division part between the first substrate 18-1 and the secondsubstrate 18-2 is illustrated to have a structure in which, forsimplification, a division surface is provided in the verticaldirection. Actually, the accurate arrangement intervals of the lightemitting diodes 16 and substrate shape are as illustrated in FIG. 4.

Light emitting diodes 16 which are adjacent across a boundary betweenthe first substrate 18-1 and the second substrate 18-2 are disposed sothat respective anodes are opposed to each other. Further, actually, thelight emitting diodes 16 which are adjacent across the boundary betweenthe first substrate 18-1 and the second substrate 18-2 are arranged soas to have, as illustrated in FIG. 4, a pitch equal to or smaller thanthat of other adjacent light emitting diodes 16 on the same substrate.

The light emitting diodes 16 mounted on the first substrate 18-1 are allarranged so that the cathodes thereof face a side opposite to the secondsubstrate 18-2. On the first substrate 18-1, the light emitting diodes16 are arranged in a direction separating from the second substrate 18-2and are electrically connected in series.

The light emitting diodes 16 mounted on the second substrate 18-2 areall arranged so that the cathodes thereof face a side opposite to thefirst substrate 18-1. On the second substrate 18-2, the light emittingdiodes 16 are arranged in a direction separating from the firstsubstrate 18-1 and are electrically connected in series.

According to this embodiment, a pair of light emitting diodes 16 havingthe smallest pitch (that is, the light emitting diodes 16 which areadjacent across the boundary between the first substrate 18-1 and thesecond substrate 18-2 (see FIG. 4)) are disposed so that respectiveanodes are opposed to each other. Therefore, the respective cathodes, atwhich heat is easily generated, are kept away from each other, and henceit is possible to avoid heat concentration. The above descriptioncorresponds to other embodiments similarly.

In this embodiment, all of the light emitting diodes 16 on the substrate18-1 are formed so that the anode sides thereof face the substrate 18-2.This can also be applied to the substrate 18-2.

That is, the substrate 18-1 and the substrate 18-2 are formed so thatthe respective anode sides face each other. This is because, asillustrated in FIG. 4, the light emitting diodes 16 are arranged veryclose to one another around the bonding portion of the substrate 18-1and the substrate 18-2, and hence heat is concentrated at that place.

According to this embodiment, in a part having the greatestconcentration of heat, a region is provided where the respective anodesides of the adjacent light emitting diodes 16 are opposed to eachother. In this manner, it is possible to form a region which alleviatesheat.

A first connector 19-1 is mounted on the first substrate 18-1. The firstconnector 19-1 is mounted at an end portion of the first substrate 18-1on a side opposite to the second substrate 18-2.

First cathode wiring 40 is formed on the first substrate 18-1. The firstcathode wiring 40 electrically connects the first connector 19-1 and thecathode of the light emitting diode 16 which is farthest from the secondsubstrate 18-2 among the light emitting diodes 16 electrically connectedin series on the first substrate 18-1.

First anode wiring 42 is formed on the first substrate 18-1. The firstanode wiring 42 electrically connects the first connector 19-1 and theanode of the light emitting diode 16 which is closest to the secondsubstrate 18-2 among the light emitting diodes 16 electrically connectedin series on the first substrate 18-1.

A second connector 19-2 is mounted on the second substrate 18-2. Thesecond connector 19-2 is mounted at an end portion of the secondsubstrate 18-2 on a side opposite to the first substrate 18-1.

Second cathode wiring 44 is formed on the second substrate 18-2. Thesecond cathode wiring 44 electrically connects the second connector 19-2and the cathode of the light emitting diode 16 which is farthest fromthe first substrate 18-1 among the light emitting diodes 16 electricallyconnected in series on the second substrate 18-2.

Second anode wiring 46 is formed on the second substrate 18-2. Thesecond anode wiring 46 electrically connects the second connector 19-2and the anode of the light emitting diode 16 which is closest to thefirst substrate 18-1 among the light emitting diodes 16 electricallyconnected in series on the second substrate 18-2.

The plurality of light emitting diodes 16 are respectively arranged onthe first substrate 18-1 and the second substrate 18-2 in a plurality ofrows. The first anode wiring 42 is disposed so as to pass between thelight emitting diodes 16 arranged in the plurality of rows on the firstsubstrate 18-1. The second anode wiring 46 is disposed so as to passbetween the light emitting diodes 16 arranged in the plurality of rowson the second substrate 18-2.

Modified Example of First Embodiment

FIG. 6 is a wiring diagram of the first substrate 18-1 and the secondsubstrate 18-2 of a liquid crystal display device according to amodified example of the first embodiment of the present invention.

In this modified example, first anode wiring 142 and second anode wiring146 are each wired on an outer side of the light emitting diodes 16connected in series in two rows. Specifically, the plurality of lightemitting diodes 16 are respectively arranged on the first substrate 18-1and the second substrate 18-2 in a plurality of rows. The first anodewiring 142 is disposed so as to pass one of regions opposing across allof the light emitting diodes 16 arranged in the plurality of rows on thefirst substrate 18-1. The second anode wiring 146 is disposed so as topass one of regions opposing across all of the light emitting diodes 16arranged in the plurality of rows on the second substrate 18-2. Thefirst anode wiring 142 and the second anode wiring 146 are respectivelydisposed at end portions of the substrate 18 on opposite sides. Othercontents correspond to the contents described in the above-mentionedfirst embodiment.

Second Embodiment

FIG. 7 is a wiring diagram of the first substrate 18-1 and the secondsubstrate 18-2 of a liquid crystal display device according to a secondembodiment of the present invention.

In this embodiment, the light emitting diodes 16 on the first substrate18-1 are arranged in one row. The light emitting diodes 16 on the secondsubstrate 18-2 are also arranged in one row. Other contents correspondto the contents described in the above-mentioned first embodiment.

Third Embodiment

FIG. 8 is a wiring diagram of the first substrate 18-1 and the secondsubstrate 18-2 of a liquid crystal display device according to a thirdembodiment of the present invention.

A connector 19 is mounted on the first substrate 18-1. The connector 19is mounted at an end portion of the first substrate 18-1 on a sideopposite to the second substrate 18-2. Meanwhile, a connector is notmounted on the second substrate 18-2. That is, electrical connectionwith the inverter (not shown) is achieved through the connector 19 ofthe first substrate 18-1 with respect to both of the first substrate18-1 and the second substrate 18-2.

In this embodiment, anode wiring 48 is formed on the first substrate18-1 and the second substrate 18-2. The anode wiring 48 electricallyconnects the connector 19 and the anode of the light emitting diode 16which is closest to the second substrate 18-2 among the light emittingdiodes 16 electrically connected in series on the first substrate 18-1.Further, the anode wiring 48 electrically connects the connector 19 andthe anode of the light emitting diode 16 which is closest to the firstsubstrate 18-1 among the light emitting diodes 16 electrically connectedin series on the second substrate 18-2. A part of the anode wiring 48 onthe first substrate 18-1 and a part of the anode wiring 48 on the secondsubstrate 18-2 are connected by a relay connector 25.

The first cathode wiring 40 is formed on the first substrate 18-1. Thefirst cathode wiring 40 electrically connects the connector 19 and thecathode of the light emitting diode 16 which is farthest from the secondsubstrate 18-2 among the light emitting diodes 16 electrically connectedin series on the first substrate 18-1.

Second cathode wiring 144 is formed on the first substrate 18-1 and thesecond substrate 18-2. The second cathode wiring 144 electricallyconnects the connector 19 and the cathode of the light emitting diode 16which is farthest from the first substrate 18-1 among the light emittingdiodes 16 electrically connected in series on the second substrate 18-2.A part of the second cathode wiring 144 on the first substrate 18-1 anda part of the second cathode wiring 144 on the second substrate 18-2 areconnected by the relay connector 25.

The plurality of light emitting diodes 16 are respectively arranged onthe first substrate 18-1 and the second substrate 18-2 in a plurality ofrows.

The anode wiring 48 and the second cathode wiring 144 are disposed so asto pass one of regions opposing across all of the light emitting diodes16 arranged in the plurality of rows on the first substrate 18-1 and thesecond substrate 18-2. The anode wiring 48 and the second cathode wiring144 are arranged in parallel on the first substrate 18-1.

Modified Example of Third Embodiment

FIG. 9 is a wiring diagram of the first substrate 18-1 and the secondsubstrate 18-2 of a liquid crystal display device according to amodified example of the third embodiment of the present invention.

In this modified example, anode wiring 148 is disposed so as to passbetween the light emitting diodes 16 arranged in the plurality of rowson the first substrate 18-1, which is different from the above-mentionedthird embodiment. Other contents correspond to the contents described inthe above-mentioned third embodiment. For example, also in this modifiedexample, the plurality of light emitting diodes 16 are respectivelyarranged on the first substrate 18-1 and the second substrate 18-2 in aplurality of rows. Further, the second cathode wiring 144 is disposed soas to pass one of regions opposing across all of the light emittingdiodes 16 arranged in the plurality of rows on the first substrate 18-1and the second substrate 18-2.

By incorporating the liquid crystal display device described in any oneof the embodiments described above, a television set can be formed,which receives radio waves for television broadcast to display imagesand output sound. Hereinafter, a liquid crystal television set isdescribed as an example.

Fourth Embodiment

FIG. 10 is an exploded perspective view of a liquid crystal televisionset according to a fourth embodiment of the present invention. FIG. 11is a view illustrating members provided behind a reflection sheet of theliquid crystal television set illustrated in FIG. 10. FIG. 12 is a sideview of the liquid crystal television set illustrated in FIG. 10. FIG.13 is a schematic view of a vertical cross section of the liquid crystaltelevision set illustrated in FIG. 10.

The liquid crystal television set includes a liquid crystal displaypanel 900 having a horizontally long screen. The screen of the liquidcrystal television set has an aspect ratio (ratio of horizontaldimension to vertical dimension) of 16:9. The liquid crystal displaypanel 900 has a front side (side on which an image is displayed)supported by an upper frame 902, and a rear side supported by a moldframe 904. The liquid crystal television set includes a backlight unit906, which is overlapped by the liquid crystal display panel 900.

The liquid crystal display panel 900, the upper frame 902, the moldframe 904, and the backlight unit 906 are stored in a cabinet 912including a front cabinet 908 and a back cabinet 910. The front cabinet908 is made of a resin, and the back cabinet 910 is made of ironsubjected to coating. The cabinet 912 is supported by a stand 918including a pedestal 914 and a leg 916. As illustrated in FIG. 12, onthe side surface of the cabinet 912, switches 920 are provided.

A cover 922 is attached to a lower rear part of the back cabinet 910. Aspeaker 924 and a circuit board 926 are disposed inside the cover 922.The circuit board 926 includes a tuned circuit (tuner) for selecting aradio wave having a specific frequency from radio waves having variousfrequencies.

The backlight unit 906 includes a reflection sheet 930 having a curvedportion 928 so that a recess surface thereof faces the liquid crystaldisplay panel 900. The curved portion 928 of the reflection sheet 930 isdisposed so as to be separated from the cabinet 912 (see FIG. 13). Thecurved portion 928 includes a first curved portion 932 and a secondcurved portion 934. The first curved portion 932 and the second curvedportion 934 are formed on respective sides of the reflection sheet 930in a vertical direction of the screen while sandwiching a plurality ofpoint light sources 936. The circuit board 926 is disposed on a lowerside of a space between the curved portion 928 and the back cabinet 910(see FIG. 13).

The backlight unit 906 includes a substrate 938 on which the reflectionsheet 930 is overlapped on a side opposite to the liquid crystal displaypanel 900 of the reflection sheet 930. A width of the substrate 938 inthe vertical direction of the screen is half the length of the screen inthe vertical direction or less. The substrate 938 is fixed to thecabinet 912. The substrate 938 may be directly fixed to the cabinet 912,or may be fixed to the cabinet 912 through intermediation of a radiatorplate 940. In the latter case, the substrate 938 is fixed to theradiator plate 940, and the radiator plate 940 is fixed to the cabinet912.

In this embodiment, at a position roughly corresponding to a center ofthe screen, the point light sources 936 including light emitting diodes942 (see FIG. 13) are mounted on the rectangular substrate 938, which islong in the horizontal direction. A printed-wiring board may be used asthe substrate 938. Fixation of the substrate 938 is performed bythreadably mounting the substrate 938 on the back cabinet 910, orthreadably mounting the substrate 938 on the radiator plate 940 made ofa metal such as aluminum and then fixing the radiator plate 940 to theback cabinet 910. The light emitting diodes 942 are arranged in astaggered pattern and in two rows in the up-and-down direction, so as toextend in the horizontal direction. When seen from the front side, adimension YL of the substrate 938 is set so as to be one-third a heightYH of the screen of the liquid crystal display panel 900 or less.

The backlight unit 906 includes the plurality of point light sources936, which are mounted on the substrate 938 and disposed so as toprotrude to the recess surface side of the curved portion 928 whilepassing through the reflection sheet 930. The plurality of point lightsources 936 are arranged in at least one row in the horizontal directionof the screen, and arranged so as to be stored within a space region,which has a width in the vertical direction of the screen, the widthbeing half the length of the screen in the vertical direction or less.Each of the point light sources 936 includes, as illustrated in FIG. 13,the light emitting diode 942 and a lens 944 disposed on the outer sidethereof. On the substrate 938, the lenses 944 each made using an acrylicresin are mounted so as to respectively cover the light emitting diodes942.

The point light source 936 emits light in a perpendicular direction tothe substrate 938 and in other directions, and light emitted in theother directions is higher in intensity than light emitted in theperpendicular direction. The lens 944 has a wide light distributioncharacteristic, which causes the light emitted from the light emittingdiode 942 to be more spread out in a viewing angle direction than in afront side direction. Such a light intensity distribution (directivitycharacteristic) of the point light source 936 is illustrated in FIG. 14.Further, FIG. 15 is a graph illustrating a measurement result ofintensity of light which exits from the lens 944. Note that, anglevalues represent angles formed between a normal to the substrate 938 anda light emission direction.

One of the features of the liquid crystal television set is high imagequality performance, which provides an impression that, although thevertical direction dimension YL of the substrate 938 is reduced to beone-third the screen dimension YH or less along the vertical directionof the screen, the screen is bright and high brightness uniformity isprovided across the entire screen.

In the conventional liquid crystal television set, a plurality ofsubstrates each including a plurality of light emitting diodes areprovided so as to obtain uniform brightness or smooth brightness changeeven in a region between the substrates. Specifically, many lightemitting diodes are used to shorten intervals between the light emittingdiodes and hence obtain smooth brightness change, and the substrates aredisposed so that each position of the individual light emitting diodescannot be optically recognized. Further, there is a case where wideintervals are provided between the plurality of substrates by disposinglenses for wide light distribution above the light emitting diodes, buteven in this case, the dimension of the substrates is larger thanone-third the screen.

In this embodiment, a dimension between outer surfaces of a pair oflenses 944 which are most separated in the vertical direction, the outersurfaces facing directions opposite to each other, is one-third thescreen dimension YH or less. When the light emitting diodes 942 arearranged in a row in the horizontal direction, a width (diameter) of thelens 944 in the vertical direction is one-third the screen dimension YHor less. In order to reduce cost, the light emitting diode 942 and thelens 944 are formed in dimensions not to extend off the substrate 938,and the dimensions thereof are set to the minimum.

In this embodiment, the vertical dimension YL of the substrate 938, orthe dimension between outer sides of the lenses 944 arranged in two rowsin the vertical direction, is one-third the vertical dimension of thescreen or less. Therefore, even if the number of the light emittingdiodes 942 is reduced, the screen is bright and a natural and smoothbrightness distribution is obtained. Therefore, the cost may be greatlyreduced.

In this embodiment, the curved portion 928 of the reflection sheet 930is formed so as to have a width of a length obtained by subtracting thevertical dimension YL of the substrate 938 from the dimension YH in thevertical direction of the screen (short side direction of the screen).When the width of the curved portion 928 is half the dimension YH ormore, the brightness distribution of the screen is comfortable even whenthe screen is seen from the front side. Further, the number of the lightemitting diodes 942 may be significantly reduced, and hence the cost maybe reduced. That is, the cost may be reduced by forming a region forreflection by the curved portion 928 to be larger than a region for aspace where the point light sources 936 are stored.

The light emitted from the light emitting diode 942 disposed on thesubstrate 938 is spread out by the lens 944, which is made of an acrylicresin and disposed above the light emitting diode 942. The light thusspread out has a distribution characteristic that light intensity islarger in an oblique direction than in the front side direction. Thelens 944 for wide light distribution is attached to each of theplurality of light emitting diodes 942, and hence, in a space in a rangefrom the substrate 938 to a diffusion plate 946 provided in theperpendicular direction (direction to the screen) (hereinafter, referredto as inner thickness Zd), the light radiated to a peripheral directionof the screen from the substrate 938 has higher light intensity thanthat of the light emitted to the front side. A part of the light whichexits from the lens 944 to the front side passes through the diffusionplate 946, and then is used to display an image by the liquid crystaldisplay panel 900. The rest of the light is reflected by the diffusionplate 946, and then reflected by the reflection sheet 930, to thereby beradiated to a direction different from the front side direction. A partof light radiated to a periphery of the screen after passing through thelens 944 passes through a peripheral portion of the screen by thediffusion plate 946, and other part of the light is reflected by thereflection sheet 930 having the curved portion 928 and passes throughthe diffusion plate 946 again.

As for the brightness performance of the liquid crystal television sethaving the above-mentioned structure, when the brightness measured fromthe front side is 100%, the periphery thereof is in a dark state ofabout 30%. A ratio of the brightness at the center of the screen in thefront side to the average brightness is 1.65. However, because thecurved portion 928 of the reflection sheet 930 is smoothly curved,smooth brightness change is obtained from the substrate 938 in thevertical direction of the screen. Therefore, even though the ratio ofthe central brightness to the average brightness is as large as 1.65, itis possible to provide a comfortable image because a large inflectionpoint is absent in the distribution thereof.

The fact that a comfortable and smooth brightness distribution can beobtained even though the ratio of the central brightness to the averagebrightness is 1.65 or larger represents that, conversely, it is possibleto reduce the number of the light emitting diodes 942 and narrow thewidth of the substrate 938, to thereby reduce the cost.

Note that, it is impossible to achieve the characteristic that thebrightness at the center is high and the brightness decreases withsmooth brightness distribution toward the periphery of the screen when astructure which blocks light radiation to the front side is provided. Inthis case, the center is dark, which results in uncomfortable displaydistribution. Therefore, the light emission characteristic of each pointlight source 936, which includes the light emitting diode 942 and thelens 944 near the corresponding light emitting diode 942, includes apredetermined output to the front side.

The back cabinet 910 forms the outermost surface of the liquid crystaltelevision set. The substrate 938 is threadably mounted on the radiatorplate 940. By dissipating the heat from the light emitting diodes 942 bythe substrate 938 and the radiator plate 940, the junction temperatureof the light emitting diode 942 is suppressed to a predetermined value.In a case where the specification brightness of the liquid crystaltelevision set is low, the radiator plate 940 may be omitted. In thiscase, the substrate 938 is directly fixed to the back cabinet 910. Inthis case, heat dissipation of the light emitting diode 942 is performedonly by the substrate 938, but even with the heat dissipation effect ofthe substrate 938, the junction temperature of the light emitting diode942 may be suppressed to a predetermined value.

The substrate 938 and the reflection sheet 930 are fixed at positionsnear the back cabinet 910, and hence it is possible to achieve a thinliquid crystal television set. With this structure, the thickness of theliquid crystal television set may be reduced while maintaining thecomfortable uniformity of the brightness performance.

In the conventional backlight unit structure, the substrate on which thelight emitting diodes are mounted is fixed to a back frame (not shown)of the liquid crystal display device, which is made of iron or aluminum.On the outer portion of the back frame, there are disposed a powersupply for driving the light emitting diodes and a substrate of a timingcontroller for controlling a gate signal line and a drain signal line ofthe liquid crystal display panel. The back cabinet is disposed on afurther outer portion thereof. Therefore, the television set requires,in addition to the inner thickness distance between the diffusion plateand the light emitting diode of the backlight unit, a distance providedbetween the back frame and the back cabinet, which causes the liquidcrystal television set to be thick.

In this embodiment, light, which exits from the lens 944 with a higherbrightness in the periphery than in the front side, passes through thepredetermined space (inner thickness Zd), and then passes through thediffusion plate 946 and the liquid crystal display panel 900. With this,an image is displayed. The substrate 938 is brought into contact withthe radiator plate 940, and the radiator plate 940 and the back cabinet910 are fixed to each other by a screw, and hence a space distance otherthan the inner thickness Zd is unnecessary. Therefore, the thickness ofthe liquid crystal television set may be reduced.

The reduction in thickness of the liquid crystal television set isachieved also by the disposition of the circuit board 926 including apower supply circuit, a video circuit, a tuned circuit (tuner), and atiming circuit for the liquid crystal display panel 900. Specifically,the curved portion 928 of the reflection sheet 930 is curved in adirection separating from the back cabinet 910, and hence a large spacecan be obtained between the curved portion 928 and the back cabinet 910.In the lower portion of the liquid crystal television set, the circuitboard 926 including the power supply circuit, the video circuit, thetuned circuit (tuner), and the timing circuit for the liquid crystaldisplay panel 900 is stored in a compact manner. With this, a space isunnecessary between the back cabinet 910 and the substrate 938 on whichthe light emitting diodes 942 are mounted or the radiator plate 940.

Next, manufacturing steps of the liquid crystal television set aredescribed with reference to FIG. 10. A wall-mount bracket 948 isattached to the back cabinet 910 from the inner side thereof, the backcabinet 910 being formed by subjecting a member made of an iron materialto coating. The wall-mount bracket 948 reinforces the strength of theback cabinet 910. Screw receiving holes are formed in the wall-mountbracket 948, which are used when the liquid crystal television set ismounted on the wall from the rear side of the back cabinet 910. Theradiator plate 940 is fixed to the inner side of the back cabinet 910,the radiator plate 940 being made of an aluminum material.

Next, the substrate 938 on which the light emitting diodes 942 aremounted is attached to the radiator plate 940. On each of the lightemitting diodes 942, the acrylic lens 944 for wide light distribution iscapped, and the lens 944 is fixed by an adhesive. Depending on thebrightness specification of the liquid crystal television set, whenthere is a margin in the junction temperature of the light emittingdiode 942, the substrate 938 may be directly attached to the backcabinet 910. Here, a white resist is applied onto the substrate 938 sothat light emitted from the light emitting diodes 942 can easily performsuccessive reflection on the surface of the substrate 938.

Next, the reflection sheet 930 is attached, which has a surface withlight diffusion property, is curved in the vertical direction of thescreen, and has holes larger in diameter than the lens 944 so as toinsert the lenses 944 therethrough. Above the reflection sheet 930, thediffusion plate 946, a prism sheet 950, and a diffusion sheet 952, eachhaving a thickness of 1.5 mm to 3 mm, are disposed. In the space (innerthickness Zd) between the substrate 938 and the rear surface of thediffusion plate 946, direct light from the light emitting diodes 942 andreflected light, which is secondary light, from the reflection sheet 930are combined.

Next, the optical sheet group is fixed by the mold frame 904, which ismade of a resin material and divided in quarters. Above the mold frame904, the liquid crystal display panel 900 is disposed. The liquidcrystal display panel 900 includes two glass substrates and liquidcrystal sealed therebetween. One substrate (TFT substrate) includes thinfilm transistors (TFTs), drain signal lines, and gate signal lines, andthe other substrate includes a color filter. The gate signal lines andthe drain signal lines formed on the TFT substrate are pulled outside tobe connected to a driver IC and a drain substrate on which the driver ICis mounted. On each surface of the glass substrates, a polarizing plateis adhered. The drain substrate is electrically connected to the timingcontrol circuit for supplying the video signal via a flexible cable.Above the liquid crystal display panel 900, the upper frame 902 made ofiron is attached, for blocking electromagnetic waves from the driver ICand fixing the liquid crystal display panel 900.

In order to finally complete the liquid crystal television set, thefront cabinet 908 made of a resin material is attached to the surface ofthe upper frame 902. On the lower side of the cabinet 912, a controlcircuit for the light emitting diodes 942, a timing control circuit, apower supply circuit for supplying power to the video circuit, aconnection terminal to the outside, and the like are disposed, and thecover 922 for protection, which is made of a resin, is attached.

The present invention is not limited to the embodiments described above,and various modifications may be made thereto. For example, thestructures described in the embodiments may be replaced by substantiallythe same structure, a structure having the same action and effect, and astructure which may achieve the same object.

What is claimed is:
 1. A liquid crystal display device, comprising: aliquid crystal display panel; and a backlight unit; wherein thebacklight unit comprises: a plurality of light emitting diodes eachhaving an anode and a cathode; a first substrate; and a secondsubstrate, the plurality of light emitting diodes being mounted on thefirst substrate and the second substrate; the first substrate and thesecond substrate are disposed adjacent to each other; and a first lightemitting diode of the plurality of light emitting diodes mounted on thefirst substrate and a second light emitting diode of the plurality oflight emitting diodes mounted on the second substrate which are adjacentacross a boundary between the first substrate and the second substrateare disposed so that respective anodes of the first and second lightemitting diodes are opposed to each other and have a pitch equal to orsmaller than a pitch of other light emitting diodes of the plurality oflight emitting diodes mounted on the first and second substrates; theplurality of light emitting diodes are respectively arranged on thefirst substrate and the second substrate in a plurality of rows; firstanode wiring is disposed so as to extend along a region which opposesthe plurality of light emitting diodes arranged in the plurality of rowson the first substrate; and second anode wiring is disposed so as toextend along a region which opposes the plurality of light emittingdiodes arranged in the plurality of rows on the second substrate.
 2. Aliquid crystal display device, comprising: a liquid crystal displaypanel; and a backlight unit; wherein the backlight unit comprises: aplurality of light emitting diodes each having an anode and a cathode; afirst substrate; and a second substrate, the plurality of light emittingdiodes being mounted on the first substrate and the second substrate;the first substrate and the second substrate are disposed adjacent toeach other; and a first light emitting diode of the plurality of lightemitting diodes mounted on the first substrate and a second lightemitting diode of the plurality of light emitting diodes mounted on thesecond substrate which are adjacent across a boundary between the firstsubstrate and the second substrate are disposed so that respectiveanodes of the first and second light emitting diodes are opposed to eachother and have a pitch equal to or smaller than a pitch of other lightemitting diodes of the plurality of light emitting diodes mounted on thefirst and second substrates; the plurality of light emitting diodesmounted on the first substrate are arranged in a direction separate fromthe second substrate and are electrically connected in series; theplurality of light emitting diodes mounted on the second substrate arearranged in a direction separate from the first substrate and areelectrically connected in series; a connector, which is mounted at anend portion of the first substrate on a side opposite to the boundary;anode wiring, which is formed on the first substrate and the secondsubstrate so as to electrically connect the connector and the anode ofthe first light emitting diode which is closest to the boundary amongthe plurality of light emitting diodes electrically connected in serieson the first substrate and so as to electrically connect the connectorand the anode of the second light emitting diode which is closest to theboundary among the plurality of light emitting diodes electricallyconnected in series on the second substrate; first cathode wiring, whichelectrically connects the connector and the cathode of the lightemitting diode which is farthest from the boundary among the pluralityof light emitting diodes electrically connected in series on the firstsubstrate; and second cathode wiring, which is formed on the firstsubstrate and the second substrate so as to electrically connect theconnector and the cathode of the light emitting diode which is farthestfrom the boundary among the light emitting diodes electrically connectedin series on the second substrate.
 3. The liquid crystal display deviceaccording to claim 2, further comprising a relay connector, whichconnects a part of the anode wiring on the first substrate and a part ofthe anode wiring on the second substrate and connects a part of thefirst cathode wiring on the first substrate and a part of the secondcathode wiring on the second substrate.
 4. The liquid crystal displaydevice according to claim 2, wherein: the plurality of light emittingdiodes are respectively arranged on the first substrate and the secondsubstrate in a plurality of rows; and the anode wiring and the secondcathode wiring are disposed so as to extend along a region which opposesthe plurality of light emitting diodes arranged in the plurality of rowson the first substrate and the second substrate.
 5. The liquid crystaldisplay device according to claim 2, wherein: the plurality of lightemitting diodes are respectively arranged on the first substrate and thesecond substrate in a plurality of rows; the anode wiring in disposed soas to extend between the plurality of rows of the plurality of lightemitting diodes on the first substrate; and the second cathode wiring isdisposed so as to extend along a region which opposes one of regions theplurality of light emitting diodes arranged in the plurality of rows onthe first substrate and the second substrate.
 6. The liquid crystaldisplay device according to claim 3, wherein: the plurality of lightemitting diodes are respectively arranged on the first substrate and thesecond substrate in a plurality of rows; and the anode wiring and thesecond cathode wiring are disposed so as to extend along a region whichopposes the plurality of light emitting diodes arranged in the pluralityof rows on the first substrate and the second substrate.
 7. The liquidcrystal display device according to claim 3, wherein: the plurality oflight emitting diodes are respectively arranged on the first substrateand the second substrate in a plurality of rows; the anode wiring isdisposed so as to extend between the plurality of rows of the pluralityof light emitting diodes on the first substrate; and the first cathodewiring and the second cathode wiring are disposed so as to extend alonga region which opposes the plurality of light emitting diodes arrangedin the plurality of rows on the first substrate and the secondsubstrate.